Existing microwave antennas include a wide variety of configurations for various applications, such as satellite reception, remote broadcasting, or military communication. The desirable characteristics of low cost, light weight, low profile and mass producibility are provided in general by printed circuit antennas. The simplest forms of printed circuit antennas are microstrip antennas wherein flat conductive elements, such as monopole or dipole antenna elements, are spaced from a single essentially continuous ground plane by a dielectric sheet of uniform thickness. An example of a microstrip antenna is disclosed in U.S. Pat. No. 3,995,277 to Olyphant.
The antennas are designed in an array and may be used for communication systems such as identification of friend/foe (IFF) systems, personal communication service (PCS) systems, satellite communication systems, and aerospace systems, which require such characteristics as low cost, light weight, low profile, and a low sidelobe. The bandwidth and directivity capabilities of such antennas, however, can be limiting for certain applications.
The use of electromagnetically coupled dipole antenna elements can increase bandwidth. Also, the use of an array of dipole antenna elements can improve directivity by providing a predetermined maximum scan angle.
However, utilizing an array of dipole antenna elements presents a dilemma. The maximum grating lobe free scan angle can be increased if the dipole antenna elements are spaced closer together, but a closer spacing can increase undesirable coupling between the elements, thereby degrading performance. This undesirable coupling changes rapidly as the frequency varies, making it difficult to maintain a wide bandwidth.
One approach for compensating the undesirable coupling between dipole antenna elements is disclosed in U.S. Pat. No. 6,417,813 to Durham, which is incorporated herein by reference in its entirety and which is assigned to the current assignee of the present invention. The Durham patent discloses a wideband phased array antenna comprising an array of dipole antenna elements, with each dipole antenna element comprising a medial feed portion and a pair of legs extending outwardly therefrom.
In particular, adjacent legs of adjacent dipole antenna elements include respective spaced apart end portions having predetermined shapes and relative positioning to provide increased capacitive coupling between the adjacent dipole antenna elements. The increased capacitive coupling counters the inherent inductance of the closely spaced dipole antenna elements, in such a manner as the frequency varies so that a wide bandwidth may be maintained.
However, the increased capacitive coupling associated with the shaping and positioning of the respective spaced apart end portions of adjacent legs of adjacent dipole antenna elements is dependent on the properties of adjacent dielectric and adhesive layers that are included in the phased array antenna. Consequently, these layers have an effect on the performance of the phased array antenna.